Lag fuse



Sept 7, 1954 G. F. LAING 2,688,677

LAG FUSE Filed April 16, 1952 fllig/1111144 45 Patented Sept. 7, 1954LAG FUSE Gordon F.'Laing, Delavan, Wis., assignor to Economy -Fuse andManufacturing Co., Chicago, Ill., `a corporation of Illinois ApplicationApril 16, 1952, Serial No. 282,602

(Cl. 20D-123) Claims. l

VThis invention .relates to time lag fuses, and

,more especially to such fuses of the dual element type applicable tolow amperage circuits,

as, for example, ratings below three amperes,

although it is not necessarily limited thereto.

v.In certain o'f its aspects, fuses of this invention follow theconsiderations of construction and operation rpresented in mycontemporary 'United States 'Patent No. 2,543,245, issued on February27, 1951, and No. 2,613,297, issued to me on October 7,1952,respectively.

In the main, the present invention combines ,the positive-actingmassive, relatively-movable,

non-fusible heat storage elements ofthe latter patent, with an improvedpositive heater means assembly as disclosed in the kformer patent, forcommunicating heat to said heat storage elements.

There results from this an improved fuse which maybecritically adaptedto open circuit upon attainment of preselected current-timerelationships without encountering objections of uncertainty andimprecision attributed to earlier embodiments, including those of theiusible type.

Other objects and advantages will become apparent hereinafter `when thefol-lowing description is read in conjunction with the accompanyingdrawings, in which- Figure 1 is a mid-sectional plan view of a fusek.cxmstructionzin accordance lwiththe present in- -vention :shown withits Aparts in closed circuit position;

Figure 2 is a side elevational view of the device of Figure 1, shownpartly in section, with the parts in open circuit position; and

Figure 3 is a modication of the heating unit employed in the foregoingembodiment.

Referring now to Figures 1 and 2, there is provided the usual insulatorcasing I0 of nber or other suitable material, having metal cap terminalsI2 and I4 which close the ends thereof, and at least one internalpartition I6, which divides the interior of the casing into twochambers.

As viewed in Figures 1 and 2, the right hand chamber contains a fuselink I8 which extends from the terminal I4 to which it is soldered,through the partition I6, into the left hand chamber, where it is bent90 degrees, and is staked to one of the massive electric conductors 20.The right hand chamber containing the fuse link I8 is preferably lledwith quenching power I9 in the usual way.

A metal plunger'1 element 22 is arranged in telescoping relation withthe conductor 20 and is adapted to reciprocate back and forth withrespect thereto so as to extend over to a metallicsleeve 24, to which itis secured by means Yoi solder 26, preferably oi a eutectic alloy ofpredetermined melting point.

A resistance wire or heater coil 28 is soldered to kthe terminal cap i2at its outer end and is soldered to the plunger 22 at the point whereits Vterminal convolution passes through an aperture inthe metallicsleeve 2d provided therefor. All of these parts are soldered to theplunger so as 'to provide a union that is eiiicient in transmitting bothelectrical energy and mechanical energy expressed as heat.

Concentrically arranged between the coil 28 and the metallic sleeve 24is an insualting lining 30, which is of material, such as porcelain,that is capable of conducting heat while at the same --time is aninsulator to electricity. The liner 30 electrically isolates the coil 28from the metallic sleeve 24 to `prevent the coil from becomingshort-circuited, and also spaces the sleeve from the terminal I2 by aprojecting end portion 32 provided for this purpose.

With the parts in closed circuit position, the plunger 22 is held inengagement with the metallic sleeve 24 by the eutectic alloy solderplaced at points 26 and 21 against the bias of a tension spring 34 whichtends to urge the plunger away iro-inthe metallic sleeve 42li and intoopen circuit position, as shown in Figure 2.

Where a surge of current passes through the fuse that exceeds thecapacity of the fuse link I8, the latter is adapted instantaneously toblow out. On the other hand, where the overload is of a magnitude whichcan be immediately tolerated, but is greater than the intended circuitcapacity over prolonged periods oi time, and is less than will causeinstantaneous failure of the fuse link I8, the current passing throughthe wire coil 28 gradually heats the latter. The heat in the coil iscommunicated through the porcelain lining 30 to the metalic sleeve 24,where it is collected and transmitted to the plunger and associatedparts until the temperature thereof exceeds the melting point of theeutectic solder.

At such point, the plunger 22 is released and the spring 34 causes it toretract from the metallic sleeve 24 into the massive metallic member 2U,to open the circuit. In this relationship, the parts appear as shown inFigure 2.

In Figure 3, there is illustrated a modified form of the invention. Herethe wire coil is replaced by a wire 38 of higher resistance, inasmuch asit is straight and thus offers a shorter path of now to the current thanin the case of the coil 28. The metallic sleeve 40 may be made tubularin form without regard to cupping or :daring the ends, except for theflange 42, which is soldered to the plunger 22 in a manner similar tothat previously described.

It is preferred that the resistance Wire 38 be accommodated in arecessed portion 44 in the head of the plunger 22 so as to affordmaximum contact with the latter, after passing through which the end ofthe wire projects through an opening in the sleeve as at 46, similar tothe construction previously described.

All of these parts are soldered together. The Wire 38 joins the terminalI2 with the plunger, but is electrically isolated from the sleeve 40 bythe heat conducting, electrically-insulating liner 48, which abutsagainst the plunger at one end,

but Which projects sufficiently beyond the sleeve at its other end tomaintain clearance between the terminal I2 and the end of the sleeve, asis indicated at 50.

This modied embodiment of heater is applied to the other parts as shownin Figures 1 and 2 in the manner and for the purpose previouslydescribed, whereby it is unnecessary to repeat the descriptionpertaining thereto.

Fuses constructed in accordance with the present 'invention have theadvantage of affording a positive source of heat from the heater unitwhich may be made effectively to control the operating conditions andperiods of time in which the lag elements will be activated to opencircuit position.

The heat generated in the heater unit upon overload is efficientlycollected and transmitted to the massive members 28 and 22, which areadapted to store predetermined amounts of sensible heat before thetemperature of all of the parts attains the fusion point of the eutecticalloy solder.

Great accuracy of performance and precision of control of circuitconditions are thus realized, Which have not heretofore been possible infunctionally similar fuse constructions known to the prior art.

I claim:

1. A lag fuse construction comprising a pair of terminals, a heaterconnected to one terminal, a fuse link secured to the other terminal, apair of massive relatively movable heat and electric current conductors,a spring associated with said conductors, fusible material holding saidconductors in expanded condition against the bias of said spring inbridging relation between said heater and fuse link, said heatercomprising a resistance Wire extending between the adjacent terminal andconductor, a non-metallic heat transmitting envelope for said wire, andmeans in surrounding relation to said envelope for collecting andtransmitting heat resident in said envelope to said adjacent conductor.

2. The invention of claim 1, in which said resistance wire is in theform of a coil.

3. The invention of claim 1, in which said envelope is an electricalinsulator.

4. The invention of claim 1, in which said envelope is porcelain.

5. The invention of claim 1, said collecting means comprising a metallicsleeve of high heat conductive properties.

6. A lag fuse comprising a pair of terminals, a fuse link connected toone terminal, a heater link connected to the other terminal, a spring lactuated plunger extending between said links and connected to one ofthem by fusible material, said heater link comprising a resistance Wireextending lbetween the terminal and plunger, a heat conductive ceramicsleeve surrounding said wire, and a metallic envelope enclosing saidsleeve in electrically insulated relation to said terminal and wiredetachably joined to said plunger in heat transmitting contact with thelatter and with said ceramic sleeve.

7. The invention according to claim 6, in which the detachable jointbetween said envelope and plunger is comprised of a eutectic solder ofpredetermined low melting point.

8. The invention according to claim 7, said resistance wire being in theform of a coil coaxially disposed in said sleeve and envelope.

9. The invention according to claim 8, said fuse link being permanentlyelectrically connected to said plunger.

10. The invention according to claim 9, said ceramic sleeve being of aporcelain-like material which is an insulator for electricity andconductor of heat.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 546,475 Potter Sept, 17, 1895 1,265,576 Wright May 7, 19182,281,795 Pittman et al. May 5, 19,42

